DE 199 03 439 A1 describes a procedure and device for operating a combustion engine, in whose exhaust gas area a SCR-catalyst (selective-catalytic-reduction) is arranged, which reduces the nitrous gases that are contained in the exhaust gas of the combustion engine with a reagent into nitrogen. The metering of the reagent or a preliminary stage of the reagent preferably takes place depending on parameters of the combustion engine, as for example the engine speed and the injected fuel quantity. Furthermore the metering preferably takes place depending on exhaust gas parameters, as for example the exhaust gas temperature or the operating temperature of the SCR-catalyst.
The reducing agent ammoniac, which can be won from a urea/water solution as a preliminary stage of the reagent, is for example provided as the reagent. The metering of the reagent or the preliminary stage has to be determined accurately. Too low metering causes nitrous gases in the catalyst not to be able to be completely reduced anymore. Too high metering causes a reagent slip, which can cause unnecessarily high reagent consumption on the one hand and depending on the consistency of the reagent an unpleasant odor nuisance on the other hand.
The determination of the reagent rate or the reagent dosage amount can take place according to EP 1 024 254 A2, based on an operating parameter of the combustion engine, as for example the fuel injection quantity and/or the engine speed and at least one parameter of the exhaust gas if necessary, as for example the exhaust gas temperature.
DE 196 36 507 A1 describes a procedure for controlling a combustion engine, at which at least one fuel after-injection is provided, which introduces oxidized exhaust components into the exhaust gas area of the combustion engine, which shall react exothermically in the exhaust gas area, in order to increase the exhaust gas temperature or at least to heat a component part. If only a small fuel amount shall be injected in the scope of the fuel after-injection, which cannot be shown anymore by the fuel injection valve, it is provided that only at each n-th fuel metering a fuel after-injection takes place.
DE 103 01 821 A1 describes a procedure for controlling an electromotor with a pulse-width modulated signal, which provides a default cycle duration and a certain duty cycle, which determines the performance or the engine speed of the engine. The cycle duration of the pulse-width modulated signal is modified depending on the duty cycle. Thereby it is ensured, that for each possible duty cycle the cycle duration is chosen in such a way that requirements regarding the power loss and requirements regarding the grid-bound failures are complied with.
EP 840 430 A1 describes a servo-drive, which is controlled by a three-phase pulse-width modulated signal. Provided are dead-times between the switch-on time and the switch-off time, whereby the dead times are variable, so that a modification of the switch-on time at a fixed cycle duration does not cause a corresponding modification of the switch-off time in all operating statuses. Thereby a more dissolved duty cycle can be achieved at a default cycle duration of the pulse-width modulated signal.
DE 37 10 467 A1 describes a fuel injection valve, which contains a core that is surrounded by an electromagnetic solenoid as well as a armature that interacts with the core and that is connected with a valve needle. When switching the electromagnet on it attracts the armature and enables thereby an opening for metering the fuel that is under pressure so long until the electromagnet is switched off.
DE 34 26 799 C2 describes a procedure for determining the opening point of time of a solenoid valve, from which on the solenoid valve is completely opened. The opening point of time is determined with the aid of the inductance change, which results from the attraction movement of the valve needle that is fixedly connected to the armature of the electromagnet, after switching on the electromagnet by changing the geometric proportions.
The invention is based on the task to provide a procedure for operating a metering valve, which is metering a reagent or a preliminary stage of a reagent into the exhaust gas area of a combustion engine, and a device for implementing the procedure, which enable a metering as exact as possible especially at lower dosage amounts or dosage rates.